Thanks! I think it definitely is the base game though - I bodged in some code to re-chart chunks in front of the current train, which seems to solve the problem. Not sure if this is something the devs would consider changing, but in my mind if the cutscene can see everywhere regardless of radar coverage, it should hear everywhere as well!
I did notice another small issue: with this mod enabled, pressing Alt+A to get a spidertron remote also results in the player/camera moving left. Oddly Alt+D doesn't have the same issue.